Talk:Ultra-high-energy cosmic ray

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Contents 1 hyphens 2 fastball? 3 Scientific joke? 4 Deflection 5 46 nanometers? 6 How fast, and what is it? 7 Pitch Speed 8 Move to UHECR 9 If it hit a human? 10 Mass

[edit] hyphens

The hyphens seemed more common, and "particle" lower-case seems more consistent with other particles, that's about as deep a reasoning as I have for this particular choice of name. Stan 06:29, 24 May 2004 (UTC)

BTW, this article demonstrates the evils of orphans; I remembered reading the first article, but had a terrible time finding it. Finally located it in the list of links to Salt Lake City. Stan 06:34, 24 May 2004 (UTC)

I've added a back-link from the GZK limit page, which should make it at least a little more accessible. --Christopher Thomas 07:02, 27 Feb 2005 (UTC)

[edit] fastball?

I think the use of fastball gives this piece a look as if it was a joke, can it be re-written slightly more formally? Cokehabit 12:17, 24 Feb 2005 (UTC)

The article first describes it as 3 × 10²⁰ electronvolts, then 50 joules, and only after those formal measures does it compare it to a fastball. Since an average everyday joe off the street is unlikely to have an intuitive grasp of what those first two measures are like I think it's quite useful to have a comparison to an everyday event like this. Bryan 17:34, 7 May 2005 (UTC)

Are you talkign about a baseball batted fastball..? It is unclear for non americans. --Procrastinating@^talk2me 14:14, 28 January 2006 (UTC)

That is why fastball is linked, you can click on it and learn everything you ever wanted to know. :) Bryan 20:44, 28 January 2006 (UTC)

Comparing the energy fo UHECRs to a fastball is a somewhat standard practice, from what I've seen. In the same way a parsec is described as "about three light years," UHECRs are given a value that helps everyone understand the energies involved.

[edit] Scientific joke?

If I have to use the sentence above - in particle physics I am one of those "joe off the street". However scientist tend to publish scientific jokes sometimes. Is this event confirmed by an independent source or it happened only for a short period in 1991 and only in particular region of Utah? The whole story and the name suggest more towards a joke. A real particle will not be only dubbed but will also be named. All the sources I was able to find through Google sooner or later go to fourmilab.ch. This is a site of an entusiast and not a scientific magazine (as it says in the faq - fermilab is in the other hemisphere). So please provide some verifiable sources. TIA, Goldie (tell me) 18:17, 13 December 2005 (UTC)

I think the article mentions something about a proton or so, never heard of this one...gotta be a joke. In good meaning, i recommend to first get acquainted "how to search the internet" -> google it up. Slicky 09:55, 28 February 2006 (UTC)

This is not a new _type_ of particle. This is an ordinary particle (either a proton or an atomic nucleus) moving at speeds more extreme than we've seen just about anything move at. Particles _moving in this manner_ are (whimsically) dubbed "oh-my-god particles". Whimsical naming in this manner is common in science. A relatively recent example is the "sonic hedgehog" gene in fruit flies (one of a series of "hedgehog" genes, named because they produce spiky-looking development defects), but even the names of the quarks show this (up, down, strange, charm, bottom, and top, with the last two formerly called "beauty" and "truth"). --Christopher Thomas 06:08, 1 March 2006 (UTC)

Definitely NOT a joke. The name "Oh-My-God" particle was clearly meant to be humorous, but there really have been detections of ultra high energy cosmic rays, which scientists are currently studying. See, for instance:

http://www.sciencemag.org/cgi/content/full/288/5469/1147a

http://prola.aps.org/abstract/PRD/v34/i5/p1622_1?qid=75ae0aca4f0202c0&qseq=15&show=10

http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PRLTAO000092000015151101000001&idtype=cvips&gifs=yes

-- tim314

Though these might be valid sources they all require payment:

• "The content you requested requires a subscription to this site or Science Pay per Article purchase. "
• "Access to PROLA requires a subscription. PROLA subscriptions are separate from the subscriptions to the current content journals."
• "If you are not a registered subscriber but would like to purchase this article, use ..."

Regardless whether it would be 1p or 1 million, I do not want to pay just to verify a scientific joke (or a nickname). So I still consider the information unconfirmed. For some reasons I am calling the proton a proton, and am not considering it a different particle than the ... proton. If those scientific journals state just a high-energy proton was detected, this whole article ought to be merged as a section at Proton. -- Goldie (tell me) 17:28, 30 March 2006 (UTC)

Merging it with proton makes no sense. If it was merged anywhere, it would be with cosmic ray, because it _is_ an extreme example of a cosmic ray. As for the validity of the term, it's used by two of the sources cited in the article. Searching on Google for '"oh my god particle" -wikipedia' (to exclude references sourced from Wikipedia) gives 30,000 hits, indicating that the term is at minimum in common use by laymen and popular press. It appears to have entered popular press via an article written by John Walker discussing the U of Utah detection results. --Christopher Thomas 18:01, 30 March 2006 (UTC)

It still strikes me that people tend to rely on Google for counting but are reluctant to rely on counters for ... er, searching. Moreover using the stated ("oh my god particle" -wikipedia) search pattern produced here only 482 hits. As I am not accessing Google from China, the politically-correct filtering ought not to apply. It was even more weird to me that one of the first-page hits was derived from Wikipedia, was admitting the fact, but Google still have put it in the list. As few hundreds seemed to me still unmanageable I've ruled out "fourmilab" citations too and tried some one-by-one checks.

From what I've seen all references were rumors repeating the rumor (all that very famous John Walker article), and all was based on one-and-only observation! This article here is talking about "at least fifteen similar events confirming the phenomenon" but references do not show any!?! OTOH I've seen numerous theories about the particle type (an example: neutrino coliding to anti-neutrino and emitting some others) but the article is certain it "was" proton. If we look at Vela Incident article, it is talking about much easy verifyable matter but is employing much more cautious approach. Maybe some people understand the Oh My God Almighty and His particles much better than His creatures. -- Goldie (tell me) 11:48, 3 April 2006 (UTC)

Just did the search again. Still got "about 30,000" as the hit count. Try it yourself if you like. If you want more observations, follow the links in this article and elsewhere to the AGASA and Fly's Eye detector pages, and look through their publications. One particle with an energy of 3e+20 eV was detected, but many others in the 1e+19 range were also picked up. If you want to fix citations in the article to better reference these, go ahead, but I don't see a problem with the article as it presently stands. --Christopher Thomas 18:46, 3 April 2006 (UTC)

"might be" valid sources? What are you suggesting, that I'm trying to trick you? You are clearly not a practicing physicist, or you would recognize the journals Science and the Physical Review. These are some of the most well known journals of physics (follow the links to their Wikipedia article if you don't believe me.) I appologize for the fact that access to scientific journals generally isn't free, but there's nothing I can do about that. Anyone who does have a subscription (which should be basically any practicing physicist) can easily verify that they are legit. (And if you can even get to the Abstracts for free, it seems to me this should be proof enough, given that they are located at the well-known domains of major scientific journals.) Trust me, this is a real subject of study, and not a joke.

As for the claim that it should be merged with proton, I'm afraid you are missing the point. The "Oh-My-God particle" isn't significant because it's a new kind of particle. It's significant as an old kind of particle with a shockingly high energy. The phenomenon is what's significant (and thus worthy of its own article), not the kind of particle. Similarly, if an amazing flying horse were discovered, it would make sense to give it its own article, not merely a section under horses. Tim314 00:40, 7 April 2006 (UTC)

Incidentally, Goldie, you may be having trouble finding articles on the Oh-My-God particle because that name is mostly used in the media, not in technical journals. If you want to find real journal articles, you should search for terms like "Fly Eye", "cosmic ray", and "high energy".

There's a free pre-prints archive located at www.arxiv.org. Use the search function to find physics papers with "Fly Eye" in the abstract, and you'll see tons of references to high energy cosmic ray detections. The term "Oh-My-God particle" won't appear in most of them, because that's a non-technical term mainly used with the popular press, but that's what they're talking about. Likewise, real journal articles will refer to the "Higgs boson", not the "God particle" (as it's called in the media). Physicists tend to use cutesy names to get the general public to take some interest to what are actually rather esoteric topics. Tim314 01:05, 7 April 2006 (UTC)

[edit] Deflection

"Because of its mass the Oh-My-God particle would have experienced very little influence from cosmic electromagnetic and gravitational fields..." and in the 1st external link "A particle with such energy would be deflected little by galactic magnetic fields" Is this a relativistic thing? because classically the force qv x B increases with velocity just as fast as the time spent in the field decreases with it, so deflections are the same for particles of all velocities. Thor2023 19:47, 14 December 2005 (UTC)

Yes —The preceding unsigned comment was added by 68.232.50.153 (talk • contribs) on 01:17, 10 February 2006.

To give something a bit less cryptic than anon's answer, consider that as the particle's speed approaches that of light from some observer's reference frame, its velocity doesn't change much (still approximately C), and its charge stays the same, but its mass increases drastically. Thus, the force is approximately the same, but the mass its trying to deflect grows, making the particle harder to deflect. --Christopher Thomas 04:13, 10 February 2006 (UTC)

[edit] 46 nanometers?

Not true, light moves away from everything at a constant rate, no mater what its speed, its called the theory of relativity. I think that should be fixed. —The preceding unsigned comment was added by 12.32.72.233 (talk • contribs).

True, actually, when measured from the perspective of the observer "at rest." The particle's perspective presumably remains consistent due to time dilation effects and such. Bryan 17:07, 30 March 2006 (UTC)

Special relativity does indeed ensure that views of the system from all inertial frames remain consistent. However, the value stated in the article seems to be in error. At 3e20 eV, a proton with a rest mass of 1e9 eV would be moving at about (1-3e-11) C, not the (1-5e-24) C stated. Which source was this value drawn from? --Christopher Thomas 18:07, 30 March 2006 (UTC)

This source: [1]. It shows the work used to get that figure. I'll paste it here, where's the error? Bryan 03:34, 31 March 2006 (UTC)

            M_0
   M  = ------------                                               [1]
                 v²
        Sqrt[1 - --]
                 c²

where M_0 is the particle's rest mass, 0, v is the particle's velocity, and c is the speed of light. Okay, we know that the Oh My God proton has a rest mass of about 1 GeV, and a total kinetic energy of 3×10^20 eV, so let's solve equation [1] for v, setting c to 1 to obtain velocity as a fraction of the speed of light:

v = Sqrt[m² - M_0²] / m

And thus, approximately:

v = 0.9999999999999999999999951 c

So taking 3×10^8 metres per second as the speed of light, we find that the particle was traveling 2.9999999999999999999999853×10^8 metres per second, thus 1.467×10^-15 metres per second slower than light--one and a half femtometres per second slower than light. If God's radar gun is slightly out of calibration, this puppy's gonna be doin' hard time for speeding. After traveling one light year, the particle would be only 0.15 femtoseconds--46 nanometres--behind a photon that left at the same time.

I think s/he was poitning out that the number of 46 nanometers is incorrect and should be removed entirely or stated something about if the theory of relativity didn't apply. Though while the later would be a unwise idea, they are options. Its true that light moves away from any other object at the speed of light no matter what its speed, even light itself moves away from light at the speed of light(crazy eh?). So my vote is to just remove the reference to being only 46 nanometers away and save us all one big headache. // Robert Maupin 02:00, 31 March 2006 (UTC)

But even moving at the speed of light there's still a point where the photon is only 46 nanometers away from the particle. 46 nanometers is about 1.5×10^-16 light-seconds, so if the OMG particle arrives at a detector 1.5×10^-16 seconds after the co-originating photon that means it was about 46 nanometers away when the photon hit. The theory of relativity is fine with this since it means that in the OMG particle's frame of reference the photon left it only 1.5×10^-16 seconds ago (possibly less, does length contraction figure in here or just time dilation?). Bryan 03:34, 31 March 2006 (UTC)

Going over my recollections, it looks like I'd botched last night's calculations (used a first-order formula valid only at low speeds - whoops). I've gone through the correct version, which produces an answer that agrees with the one given by John Walker. My (current, hopefully correct) calculations are as follows, for anyone who wanted to see the steps JW omitted:

1. 
2. (actually it's E + M0, but close enough)
3. (from SR; we both start with versions of this)
4. 
5. 
6. 
7. (this is equivalent to JW's ending formula)
8. (first-order expansion of square root of (1-x) is 1 - (1/2)x, valid because x is much smaller than 1 in this case)
9. 
10. 

...And this is close enough to the 5e-24 value the article cites, which is consistent with a lag of about 50 nm.

So in summary, I goofed about the values. Sorry for the trouble.

Per the original thread, all of this is consistent with SR, and nobody who replied (including me) said otherwise. Part of the point of relativity is that all observers see light as moving at C, regardless of their motions with respect to each other. An observer on earth sees the particle travel for a year and arrive 50 nm behind a photon emitted at the same place and time. An observer sitting on the particle sees the photon receding at C, but sees a much shorter time between emission and detection, making the viewpoints consistent with each other. --Christopher Thomas 05:53, 31 March 2006 (UTC)

[edit] How fast, and what is it?

"The Oh-My-God particle is a proton with the energy of a slow-pitched baseball. And it's moving so fast that after travelling for a year, it would only be a few nanometers behind a photon travelling at the speed of light." [2] OK not an authoratative source, but can someone check the energy calculation? Rich Farmbrough 21:18 30 March 2006 (UTC).

Already done for distance (see above). One light-year is about 9e15 m, so at (1-3e-11) C, it'd lag the photon by about 300 km. The value given in press releases, (1-5e-24) C, gives about 50 nm (consistent with the stated distance), but I really don't see how they got that speed value (it's inconsistent with the value I get using special relativity). The energy, 3e20 eV, corresponds to about 50 J. A baseball (weighing about 0.14 kg) with that energy would be moving at about 27 m/s (about 60 mph). I'd like to see where that source got its information, as it looks like recycled press release or Wikipedia material at first glance. --Christopher Thomas 22:19, 30 March 2006 (UTC)

Update: I goofed with my original calculations. The value of (1-5e-24) C is correct, as is the 46 nm value. All other values in my previous response are correct. --Christopher Thomas 05:56, 31 March 2006 (UTC)

[edit] Pitch Speed

Personally I would like a little mroe accuracy in the speed of the basebal, there has bene alot of comments on this reference, elts see if we can clear it up and see what the speed of the baseball would be. Eg i the format of "A baseball pitched at a speed of X would..." it flows decently with the article and probably stop to many more comments being raised about it. -Robert Maupin 03:35, 12 April 2006 (UTC)

If a 150 g baseball had a kinetic energy of 50 J it would be moving about 25 m/s. Should I put that in? —Keenan Pepper 03:52, 12 April 2006 (UTC)

Sure ,it only helps.--Procrastinating@^talk2me 09:40, 12 April 2006 (UTC)

I'd found 140 g as the mass of a baseball, and got 27 m/s, and about 60 mph, as noted above. By all means put it in, but a mph conversion in parentheses is probably a good idea. --Christopher Thomas 15:46, 12 April 2006 (UTC)

[edit] Move to UHECR

Instead of having UHECR point to this article, could we move that around? "Oh-my-god" particle isn't exactly a recognized name in any literature I've read. —The preceding unsigned comment was added by 132.250.167.155 (talk • contribs) .

I agree. —Keenan Pepper 21:22, 6 June 2006 (UTC)

[edit] If it hit a human?

what would it happen if it had hit a human? at that energies it would create tremendous pressures on the skin wouldn't it? or would it just pass right through? - jak (talk) 16:01, 12 June 2006 (UTC)

Generally, a particle's chance of interacting with matter goes down as its energy goes up, so it would almost certainly just pass right through (along with the many, many other cosmic rays that pass through you every second). If it did interact with you, it would be imparting some of its energy onto an electron or other charged particle in your body, which would then cause a jet of secondary radiation, but you wouldn't notice this either (your chance of getting cancer would go up by some infinitesimally small amount). --Christopher Thomas 20:16, 12 June 2006 (UTC)

Christopher Thomas is right. I work at a gamma-ray spectroscopy lab and one of the things we constantly have to deal with is the tendency for high-energy gamma rays not to be completely absorbed by the detector, but to scatter away and leave only a small fraction of their energy, which is useless for our purposes. Even though one of the particles discussed in this article carries as much energy as a baseball, there's no way it could give any significant part of that energy to your body, so you'd never notice it. —Keenan Pepper 23:54, 12 June 2006 (UTC)

[edit] Mass

The article doesn't seem to mention its mass. Does anyone know what it is? Would I be right in thinking it's a proton or something of similar mass? raptor 11:14, 3 November 2006 (UTC)